The general aim of this one-day symposium is to provide, for the first time, an overview of our current understanding of the cellular and molecular basis of pattern formation, a field which has advanced rapidly during the last five years. Pattern formation is here broadly defined to include maternal determination, induction of organ districts, and the differentiation of tissue patterns within these districts. The specific aims of the symposium are: (1) to bring together a group of investigators who use a broad spectrum of organisms and technologies in the investigation of pattern formation; (2) to determine what common and/or different cellular and molecular themes are emerging from their studies, and how these themes might relate to formal models of pattern formation that have been proposed; and (3) to discuss new ideas that indicate the most significant directions the field will likely take. An additional aim is to reach a broad audience consisting not only of investigators who work in the field, but also those in related fields, as well as postdoctoral and graduate students. The symposium is significant to health in that the basic research findings presented may offer insights into how pattern defects arise during embryogenesis, and how those defects might be avoided or eliminated.